During operation of a boat powered by an outboard motor, it is often desirable to raise or lower the motor. For example, when operating a boat in shallow water or removing a boat from the water with a submersible boat trailer, it is often necessary to raise the motor so that the propeller and rudder are not damaged by the bottom of the body of water. In other instances, it may be desirable to raise the motor while operating the boat at high speeds to reduce the amount of drag created by the presence of the motor in the water.
Adjusting the trim or height of an outboard motor can be accomplished by manipulating a set of controls operably connected to a jack plate. Although meanings of the term jack plate can vary, for purposes of this application, jack plate refers to the interfacing apparatus between a boat and an accompanying outboard motor. Generally, a component of the jack plate is fixedly mounted to the transom of the boat, while another component is mounted to the outboard motor. By operating an actuator attached to the two components, the motor can be raised or lowered in relation to the transom. A number of different types of lift actuators have been incorporated into jack plates, such as, for example, hydraulic, electric, electro-mechanical, or strictly manually operated actuators.
Jack plates can accomplish raising or lowering the propeller of an outboard motor by pivoting the motor about a selected point, such as at or near the top of the transom. Pivoting an outboard motor to raise the motor, however, has several drawbacks. As the motor pivots, the angle at which the propeller displaces water changes, resulting in a decrease in the propulsive efficiency of the motor.
Because of the drawbacks associated with tilting outboard motors, jack plates have been developed that can raise or lower the entire outboard motor in a substantially vertical direction. For example, U.S. Pat. No. 5,782,662 discloses an hydraulically powered jack plate comprising opposing supports that incorporate linear bearings in which rides a slide which is capable of vertical movement. In such vertically actuating jack plates, the points where the bearings and the lift plate are joined typically bear much of the weight of the motor. As a motor is vertically lifted out of the water, the bearings bear an even greater load as the buoyant force of the water acting upon the motor is reduced. As a result, a drawback of existing vertically actuating jack plates is mechanical failure where the bearings are joined to the lift plate. A further drawback of existing jack plates is the presence of fastening members that can result in binding between the moving parts of the jack plate.